The present invention generally relates to fields of telecommunications and test equipment, and more particularly, to a monitoring system and method for enabling efficient monitoring of communications signals communicated along a plurality of connections. Although the monitoring system and method of the present invention are not limited to this particular application, they are particularly suited for implementation in monitoring nodes associated with a cable television network.
A television (TV) cable network, which is maintained and operated by a cable operator, generally includes a central office, oftentimes referred to as a xe2x80x9chead end,xe2x80x9d where TV signals are captured for retransmission over trunk cables and neighborhood distribution cables to cable subscribers, for example, homes, businesses, and schools. Although these networks were originally designed and implemented with coaxial cables, optical fiber is now sometimes implemented between the head end office and trunk cables, among other places. The cable head end office usually has equipment to receive terrestrial and space-based transmissions from sources (e.g., satellites) around the world. Recently, head end offices have been equipped with high-capacity connections to the Internet. Many companies in the cable television market that own and maintain these networks are currently in the process of upgrading their networks from one-way to two-way networks (a forward path outwardly and a return path inwardly) in order to offer high speed data communications to the Internet and new multimedia services, such as the ability to order specific music and movies on demand.
The forward and return paths occupy different frequency ranges. In North America, the forward path, where the television, music, or other signal channels are usually located, starts at about 55 MHz and spans across the frequency spectrum to about 750 MHz to 1 GHz. Typically, each television channel has a bandwidth of about 6 MHz. The return path is usually allocated to that region of the frequency spectrum between about 5 MHz and 42 MHz, which is inherently susceptible to noise and interference from a variety of sources, due largely to its low frequency range. The return path can support a number of different services operating within the frequency spectrum of the return path, such as Internet data, telephony, and pay-per-view, as examples.
Each of the cable services is provided via a forward and/or a return path with one or more communications devices and/or modems situated at the subscriber""s location and one or more corresponding communications devices and/or modems at the cable system""s head end office. In order to operate properly and deliver a high quality service to the end user, each of these communications devices needs, among other things, an adequate signal-to-noise (S/N) ratio (typically greater than 20-30 dB) to operate correctly. Also, it is important for the device to operate within an expected power range. Furthermore, the cable operator is also concerned with the overall power of the entire node to ensure that all of the services together do not overload the transmission facilities.
One of the biggest problems that cable TV operators encounter is noise degradation in the return path, which can have a catastrophic impact on performance. As a result, many cable operators have been focusing on carefully monitoring the signal characteristics of the return path, identifying problematic connections and components thereof, and replacing and repairing parts where necessary in order to maintain and improve the return path signal characteristics. At least one prior art system for monitoring signal channels on the various nodes, or paths on connections having one or more signal channels, of the cable network utilizes a spectrum analyzer, which plots power amplitude versus frequency. A user of these systems typically specifies, for example, by drawing on a computer screen, an alarm level limit above and/or below the frequency spectrum for an entire return path, which may have one or more signal channels. Some of these prior art systems can learn an alarm limit by recording high level and low level marks through a series of spectrum scans. The limits are taken from this information and then adjusted by the user, as needed. Alarms are triggered based on the actual power amplitude level deviating above or below the specified alarm limit(s) based on some pattern, such as multiple successive scans or percentages outside the limit. These prior art systems do not have any inherent knowledge of the signal characteristics associated with any of the services within the return path spectrum. In essence, in the foregoing systems, the systems record how the return path is actually working, and the systems attempt to keep the return path working the same way.
Although meritorious to an extent, these prior art systems are problematic and have disadvantages. They generally do not provide a mechanism for testing individual channels and measuring signal parameters, for example but not limited to, carrier-to-noise (C/N) ratio. Moreover, these prior art systems typically do not provide a measure of total node power, which is useful for ensuring proper power levels for the transmission lasers associated with the optical fibers of the cable system. Finally and perhaps most notably, the signal characteristics (e.g., center frequency, bandwidth, amplitude, etc.) of the various signal channels vary from node to node of the cable network, based in part upon (a) use of different device types (most devices burst on and off based on data traffic, while some other types of devices transmit continuous signals) and (b) failure to implement a systematic global plan, making it extremely difficult to design and implement sophisticated automated testing systems.
The present invention provides a monitoring system and method for enabling efficient monitoring of communications signals communicated along a plurality of connections. Although the monitoring system and method of the present invention are. not limited to this particular application, they are particularly suited for implementation in monitoring nodes associated with a cable television network. Notably, in connection with the monitoring system and method, the present invention provides a user friendly feature, called a total node power test, that, when used in connection with an active node, provides a general indication of the health of the node. The present invention also provides for group comparison of total node power test results collectively. A technician may use the group total node power display in troubleshooting system wide abnormalities.
The channel plan has one or more predefined specifications for each of one or more signal channels on each of the nodes. The channel plan may comprise a specification of the following, for example, for each of the channels: a label describing use of the corresponding channel, a center frequency, a bandwidth, a power level, information regarding the carrier roll-off, a default status indicator identifying whether the corresponding channel is currently allocated or reserved for future use, one or more default threshold levels for various tests, and an alternate center frequency that may be utilized by the corresponding channel. Each test plan prescribes measurement of one or more signal parameters, pertaining to one or more nodes as a whole and/or to one or more channels contained within the nodes.
The channel plan enables a monitoring system to, among other things, conduct automatic periodic test plans, comprising tests, on the nodes, based upon the predefined data specified in the channel plan. As an example of a possible implementation, the monitoring system can include a spectrum analyzer, a switch enabling the spectrum analyzer to interface with the nodes, and a controller controlling the switch and the spectrum analyzer. The controller is configured to enable creation of and display of the channel plan and test plan, based upon user inputs. The controller causes periodic automatic testing of the signal characteristics of each of the nodes based upon the test plan. The test plan may include alarm limits that are triggered and tracked when a signal parameter of a node or channel exceeds an alarm limit.
The present invention can also be viewed as providing several methods for enabling efficient monitoring of signals on nodes. In this regard, one of these methods, as an example, can be broadly conceptualized by the following steps: interfacing to signals that are communicated along a plurality of nodes, each node having one or more signal channels, all of the nodes of the plurality having their respective channels allocated according to a channel plan; and periodically testing the signals on each of the plurality of nodes by accessing a test plan, which is based upon said channel plan, and prescribing measurement of at least the total node power in accordance with the test plan. Total node power as described herein is the total power amplitude versus frequency across the frequency spectrum of the node as described by the channel plan. The total node power test provides insight into overall transponder(s) health and network node continuity.